1. Field of the Invention
The present invention relates to a cellular conductive roller used for charging, transferring, paper carriage, development, and cleaning in an image forming device using an electrophotographic process. The present invention further relates to a method for making the cellular conductive roller and an electrophotographic device using the same.
2. Description of the Related Art
Charging and discharging processes in electrophotographic processes have been carried out by using corona discharging. Ozone generated during corona discharging, however, promotes deterioration on the surface of the photosensitive member, and wire contamination, which results in some problems in image formation, such as image defects, black lines, and the like.
There has been intensive investigations on contact electrification and transferring methods to eliminate such disadvantages. Solid charging rollers made of conductive rubbers have been mainly used in the contact electrification methods, since some surface defects such as irregularity on the surface of the charging member cause a partially nonuniform charge. However, such solid rubber rollers have some problems such as charging noises because of the difficulty in the lowered roller hardness. On the other hand, the nip region, which is formed by the contact of the surfaces of the transferring roller and photoconductive drum in the transferring process, must be adjusted to an adequate hardness.
Therefore, cellular members containing dispersed conductive powder have been used as the conductive rollers instead of solid rubber rollers. Some cellular conductive rollers are made by inserting a tube made of a cellular rubber containing dispersed conductive powder into a mandrel, grinding the tube surface with an abrasive grind wheel, and removing grinds with air, a brush or the like. The resistance of the rollers made by such a process may be adjusted depending on its use by applying conductive paints on the surface.
When attempting to lower the hardness of the roller by changing the extent of foaming in the conventional cellular conductive rollers, the cell size of the cellular member must be increased. As a result, large cells appear on the surface of the roller after grinding, resulting in nonuniform contact with a photosensitive drum. Thus, such a method still retains a problem in that stable conductivity cannot be achieved.
Additionally, the conventional method set forth above has a following drawback especially in cleaning after grinding: Since cleaning by a compressed air blow or a brush after grinding is incomplete, the surface smoothness is lost on the surface of the cellular conductive roller, resulting in an unstable resistance in the area on which the roller comes in contact with a medium, a nonuniform surface smoothness and electrical resistance in spite of coating.